1. Field
The present invention relates generally to communications, and more specifically, to systems and techniques for managing code channel assignments in a wireless communications system.
2. Background
Modern communications systems are designed to allow multiple users to share a common communications medium. One such communications system is a code division multiple access (CDMA) system. The CDMA communications system is a modulation and multiple access scheme based on spread-spectrum communications. In a CDMA communications system, a large number of signals share the same frequency spectrum and, as a result, provide an increase in user capacity. This is achieved by transmitting each signal with a different code that modulates a carrier, and thereby, spreads the signal over the entire spectrum. The transmitted signals may be separated in the receiver by a correlator using a corresponding code to de-spread the desired signal. The undesired signals, whose codes do not match, contribute only to noise.
In spread-spectrum communications, a base station controller (BSC) is often used to interface a wireless network to a communications infrastructure such as a wide area network (WAN) or a local area network (LAN). The wireless network includes multiple base stations each configured to serve all users within a geographic region known as a cell. In this configuration, orthogonal sequences known as Walsh codes may be used in the forward link to separate multiple users operating within the same cellular region. The forward link refers to signal transmissions from a base station to a user.
With the tremendous increase in wireless communications over the past years, there has been a demand for higher data rate services to support web browsing, video applications, and the like. Often the demand is met by using multiple forward channels to carry traffic from the base station to a user with each forward channel having a distinct Walsh code. Unfortunately, this approach tends to introduce additional complexities in the user equipment requiring multiple Walsh code demodulation.
An alternative method for providing high data rate services that avoids the complexities of demodulating multiple Walsh channels, involves the use of spreading sequences derived from one or more Walsh codes. However, once a Walsh code is used, it cannot be used again to generate a subsequent spreading sequence for lack of orthogonality. Accordingly, an efficient methodology or algorithm is needed for spreading sequence assignments to avoid the loss of Walsh codes needed to construct higher speed channels.